1. Field of the Invention
The present invention relates to a vehicle-mounted image pickup device which captures an image of vehicle surroundings by means of introducing light entering an incident window area provided on a case member which houses an image pickup main unit.
2. Description of the Related Art
FIG. 3 is a cross-sectional view of a vehicle-mounted image pickup device of this type according to an example proposed by the present inventor. FIG. 4 is an enlarged view of the principal constituent elements shown in FIG. 3.
As shown in FIG. 3, a vehicle-mounted image pickup device comprises a lightproof case member 1 made of industrial plastic; and an image pickup device main unit 3 to be disposed within the case member 1. The vehicle-mounted image pickup device is mounted on an exterior surface of a vehicle, thereby simultaneously capturing blind spots in two directions corresponding to a driver""s blind spots among vehicle surroundings. A fixture 5 is attached to the case member 1 for use in mounting the image pickup device on the vehicle.
In a conceivable preferable mode of use of the vehicle-mounted image pickup device, the vehicle-mounted image pickup device is mounted on the front end of the vehicle (e.g., on the front grill). The image pickup device captures front left-side and right-side blind spots of the vehicle.
The image pickup device main unit 3 comprises an image pickup unit 11 and a prism (reflection means) having two reflection surfaces for reflecting, to the image pickup unit 11, a light ray 13L entering from a left-side incident window area (i.e., a blind spot region) and a light ray 13R entering from a right-side incident window area (i.e., a blind spot region). The image pickup device main unit 3 further comprises a hold member 17 for holding the prism 15, and a circuit unit 19 for driving and controlling the image pickup unit 11.
The circuit unit 19 comprises three circuit boards 21 having elements provided thereon. The image pickup 11 is disposed on the three circuit boards 21. The circuit boards 21 are provided with an unillustrated connection section to which is connected a connector 33 coupled to a distal end of a connection cable 31.
The prism 15 has a substantially a triangular prism shape. Of three side surfaces 15a through 15c, two side surfaces (15a and 15b in the present embodiment) are respectively disposed opposite a left-side translucent window 35L and a right-side translucent window 35R provided in the case member 1.
The light ray 13L that has entered the case member 1 by way of the left-side window area through the left-side window 35L enters the prism 15. The light ray 13L is reflected by a left-side side surface 15a of the prism, which serves as a reflection surface, toward the image pickup unit 11, whereby the reflected light is introduced into the image pickup unit 11. Similarly, the light ray 13R that has entered the case member 1 by way of the right-side window area through the right-side window 35R enters the prism 15. The light ray 13R is reflected by a right-side side surface 15b of the prism, which serves as a reflection surface, toward the image pickup unit 11, whereby the reflected light is introduced into the image pickup unit 11.
The light rays 13L and 13R introduced into the image pickup unit 11 enter an image pickup element 11b by way of an imaging lens 11a provided in the image pickup unit 11. As a result, images pertaining to the left-side and right-side incident window areas are formed by the image pickup element 11b. The thus-captured image is output to the outside by way of a cable 31a of a circuit unit 19 or the connection cable 31.
Here, in the window sections 35L and 35R serving as incident window areas of the case member 1, a step 40 is formed in the edge of an opening 39L and in the edge of an opening 39R at the time of formation of the openings 39L and 39R. Translucent plates 37L and 37R made of glass are fitted into corresponding steps 40. Industrial plastic having the same coefficient of expansion as that of the case member 1 can be used for the translucent plates 37L and 37R. However, if the windows 35L and 35R are flawed, images are adversely affected to a great extent. Hence, glass material which is less susceptible to flaws than industrial plastic is used for the translucent plates 37L and 37R.
In the vehicle-mounted image pickup device having the foregoing construction, if rainwater enters the case member 1, dew condenses on an optical system element provided in the image pickup unit 11, thereby deteriorating the image pickup performance. For this reason, when the translucent plates 37L and 37R are fitted to the steps 40 formed around the openings 39L and 39R of the case member 1, the inside of the case member 1 is hermetically sealed by use of an adhesive (not shown).
Reference numeral 43 provided in FIG. 3 designates a heat contraction tube for sealing the inside of a cylindrical section 45 opened in the case member 1 and the connection cable 31. Reference numeral 47 designates a sealing member for sealing a clearance between the cylindrical section 45 and the outermost coating 31b of the connection cable 31.
However, in relation to the waterproof structure according to the proposed example, the inside of the case member becomes hermetic in relation to the outside, thereby inducing a temperature difference between the inside of the case member 1 and the outside thereof. The external air pressure drops relative to the internal pressure of the case member 1 for reasons of the temperature difference. Because of this pressure difference, pressure is exerted on the openings 39L and 39R toward the outside, thereby resulting in danger of weakening the adhesive strength of the adhesive material bonding the translucent plates 37L and 37R to the case member 1.
As mentioned above, when the adhesive strength exerted between the translucent plates 37L and 37R and the case member 1 weakens over time, the air tightness of the area of reduced adhesive strength is deteriorated. As a result, water resistance of the case member 1 is impaired. In some cases, there is a fear of the translucent plates 37L and 37R dropping from the case member 1 because of vehicle vibration.
The present invention has been conceived against this back drop and is aimed at providing a vehicle-mounted image pickup device which prevents occurrence of damage to an incident window area and has superior performance in preventing deterioration in water resistance.
To solve the problem set forth, the present invention provides a vehicle-mounted image pickup device which introduces light having entered into an image pickup main body housed in the case member through an incident window area formed in a case member, thereby capturing an image relating to vehicle surroundings, wherein the case member comprises
a translucent housing whose portions corresponding to the incident window regions are sealed;
a flaw-prevention translucent plate which is stacked on areas corresponding to the incident window regions of the translucent housing and is situated on the exterior surface side; and
an opaque layer formed in an area other than the area where the translucent plate of the translucent housing is disposed.
Preferably, recesses are formed in an exterior surface of the incident window regions of the translucent housing, and the translucent plates are fitted into the recesses.
Preferably, the translucent plate is bonded to the translucent housing by means of a translucent adhesive.